from django.conf import settings as dj_settings
from django.core.signals import setting_changed
from django.utils.translation import gettext_lazy as _

from .utils import deprecate

DEFAULTS = {
    'DISABLE_HELP_TEXT': False,

    'DEFAULT_LOOKUP_EXPR': 'exact',

    # empty/null choices
    'EMPTY_CHOICE_LABEL': '---------',
    'NULL_CHOICE_LABEL': None,
    'NULL_CHOICE_VALUE': 'null',

    'VERBOSE_LOOKUPS': {
        # transforms don't need to be verbose, since their expressions are chained
        'date': _('date'),
        'year': _('year'),
        'month': _('month'),
        'day': _('day'),
        'week_day': _('week day'),
        'hour': _('hour'),
        'minute': _('minute'),
        'second': _('second'),

        # standard lookups
        'exact': _(''),
        'iexact': _(''),
        'contains': _('contains'),
        'icontains': _('contains'),
        'in': _('is in'),
        'gt': _('is greater than'),
        'gte': _('is greater than or equal to'),
        'lt': _('is less than'),
        'lte': _('is less than or equal to'),
        'startswith': _('starts with'),
        'istartswith': _('starts with'),
        'endswith': _('ends with'),
        'iendswith': _('ends with'),
        'range': _('is in range'),
        'isnull': _(''),
        'regex': _('matches regex'),
        'iregex': _('matches regex'),
        'search': _('search'),

        # postgres lookups
        'contained_by': _('is contained by'),
        'overlap': _('overlaps'),
        'has_key': _('has key'),
        'has_keys': _('has keys'),
        'has_any_keys': _('has any keys'),
        'trigram_similar': _('search'),
    },
}


DEPRECATED_SETTINGS = [
]


def is_callable(value):
    # check for callables, except types
    return callable(value) and not isinstance(value, type)


class Settings:

    def __getattr__(self, name):
        if name not in DEFAULTS:
            msg = "'%s' object has no attribute '%s'"
            raise AttributeError(msg % (self.__class__.__name__, name))

        value = self.get_setting(name)

        if is_callable(value):
            value = value()

        # Cache the result
        setattr(self, name, value)
        return value

    def get_setting(self, setting):
        django_setting = 'FILTERS_%s' % setting

        if setting in DEPRECATED_SETTINGS and hasattr(dj_settings, django_setting):
            deprecate("The '%s' setting has been deprecated." % django_setting)

        return getattr(dj_settings, django_setting, DEFAULTS[setting])

    def change_setting(self, setting, value, enter, **kwargs):
        if not setting.startswith('FILTERS_'):
            return
        setting = setting[8:]  # strip 'FILTERS_'

        # ensure a valid app setting is being overridden
        if setting not in DEFAULTS:
            return

        # if exiting, delete value to repopulate
        if enter:
            setattr(self, setting, value)
        else:
            delattr(self, setting)


settings = Settings()
setting_changed.connect(settings.change_setting)
